1. Field of the Invention
The present invention relates to a compensation circuit for compensating for the fluctuations in the intensity of the light source or for stains on the windows of cells in an analyzer.
2. Description of the Prior Art
A circuit as shown in FIG. 1 or FIG. 2 has been used as a circuit for compensating for the fluctuations in the intensity of a light source. FIG. 1 shows a circuit in which a compensating resistance VR can be adjusted by an AGC circuit (Automatic Gain Control circuit) while light passing through an object to be measured 2 from a light source 1 is detected by a detector 3. The resulting detector output signal is amplified by an amplifier 4 after passing through the compensating resistance VR and output as signal e.sub.o. According to this circuit, it is necessary to carry out an operation to adjust the resistance VR by means of the AGC circuit 5 by switching ON (i.e.--closing) a switch SW so that the output signal e.sub.o may be made equal to a standard reference voltage E.sub.s, the resistance VR being adjusted after removing the object to be measured 2 in order to compensate for the fluctuations in the intensity of the light source 1. Accordingly, it is impossible to carry out measurements on the object 2 during this adjustment operation. That is to say, this circuit has a disadvantage in that the measurements can only be carried out intermittently and fast fluctuations in the intensity of the light source cannot be sufficiently compensated for.
On the other hand, FIG. 2 shows a circuit in which a measured signal detected by a detector 3 is fed to a logarithmic amplifier 6; a monitor signal from a light source 1 is detected by a detector 3' whose output is fed to a logarithmic amplifier 7; the difference between the output signals of amplifiers 6 and 7 is determined by means of a differential amplifier 8, and the fluctuation in the intensity of the light source can be compensated for. According to this circuit, although continuous measurements are possible because the compensating operations can be carried out during measurements, it has disadvantages in that the errors are increased with a decrease in the intensity of the light source and an adequate compensation for the fluctuations in the intensity of the light source is thereby impossible; in addition, the dynamic range (i.e.--the ratio of the maximum value of the signal level which can be treated by an amplifier divided by the minimum value of the signal level thereof) is decreased because of the fact that the division of analog quantities is carried out.
Although the above-noted description relates to the compensation for the fluctuations in the intensity of a light source, a similar compensating method as that described above is used with the same disadvantages as that described above in order to compensate for stains on the windows of cells.